1. Field of the Invention
The present invention relates to an apparatus and method for achieving low growth temperature in chemical vapor deposition (CVD) and low temperature etching, and in particular to a metallorganic chemical vapor deposition (MOCVD) method that achieves low growth temperature while simultaneously allowing high-temperature cracking of growth precursors and etching at reduced substrate temperatures. The present invention is applicable to the low-temperature deposition of a variety of materials, enhancing the pyrolysis-efficiency of source gases/chemicals in chemical vapor deposition (CVD) systems, obtaining two-dimensional layered growth of many materials, as well as etching of a variety of materials.
2. Discussion of the Background
Deposition of many materials by MOCVD, also known as organometallic vapor phase epitaxy (OMVPE), is well documented. In all the previously described MOCVD growth approaches, a substrate, on which the deposition of material/materials is achieved, is kept directly on an RF-heated susceptor or on a resistively-heated susceptor. In some cases, the substrate is heated by infra-red radiation. In a typical MOCVD growth apparatus, organometallic sources and other gaseous sources tend to thermally disassociate in the vicinity of the hot susceptor, adsorb on to the substrate-surface, react and form a growing layer that is desired/intended.
For many applications, such as (1) in obtaining growth of materials which are stable only at lower temperatures, below the cracking temperature of the growth-precursors that produce the material, (2) in obtaining improved material quality by avoiding exposure of the substrate (and the growing film) to higher temperatures, (3) in obtaining improved device structures by avoiding inter-diffusion between the various deposited layers, etc., it is desirable to maintain the substrate at lower temperatures during the deposition process. This has been traditionally achieved through judicious choice of organometallic and hydride precursors, in MOCVD, which crack at lower growth temperatures so that the substrate can be maintained at lower temperatures, through mechanisms like photo-induced dissociation of precursors or through heated pre-cracking of source gases. However, while many of these approaches have had some success, many also have limitations.
For example, in the ultraviolet-photon-induced dissociation of organometallic sources in the growth of HgCdTe, unwanted homogeneous nucleation can occur leading to particulate formation in the gas-phase and therefore, poor quality epitaxial growth of HgCdTe on the substrate. Similarly pre-cracked AsH.sub.3 to produce As for GaAs growth at lower temperatures, leads to undesirable, extremely high levels of C in GaAs. Similarly, use of exotic precursors (if they can be synthesized and made stable for handling, transportation, and storage) to achieve lower growth temperatures can lead to an expensive epitaxial deposition process.